Calculation of the Microscopic and Macroscopic Linear and Nonlinear Optical Properties of Liquid Acetonitrile. II. Local Fields and Linear and Nonlinear Susceptibilities in Quadrupolar Approximation

Hyperpolarizabilities of Push-Pull Chromophores in Solution: Interplay between Electronic and Vibrational Contributions

Contemporary design of new organic non-linear optical (NLO) materials relies to a large extent on the understanding of molecular and electronic structure-property relationships revealed during the years by available computational approaches. The progress in theory-hand-in-hand with experiment-has enabled us to identify and analyze various physical aspects affecting the NLO responses, such as the environmental effects, molecular vibrations, frequency dispersion, and system dynamics. Although it is nowadays possible to reliably address these effects separately, the studies analyzing their mutual interplay are still very limited. Here, we employ density functional theory (DFT) methods in combination with an implicit solvent model to examine the solvent effects on the electronic and harmonic as well as anharmonic vibrational contributions to the static first hyperpolarizability of a series of push-pull α,ω-diphenylpolyene oligomers, which were experimentally shown to exhibit notable second-order NLO responses. We demonstrate that the magnitudes of both vibrational and electronic contributions being comparable in the gas phase significantly increase in solvents, and the enhancement can be, in some cases, as large as three- or even four-fold. The electrical and mechanical anharmonic contributions are not negligible but cancel each other out to a large extent. The computed dynamic solute NLO properties of the studied systems are shown to be in a fair agreement with those derived from experimentally measured electric-field-induced second-harmonic generation (EFISHG) signals. Our results substantiate the necessity to consider concomitantly both solvation and vibrational effects in modeling static NLO properties of solvated systems.

Spectroscopy and second hyperpolarizability of odd spin states of acetonitrile: Theoretical study

The present study reports the spectroscopic characterization and second hyperpolarizability of odd spin states of acetonitrile in gas phase and water solvent. The odd spin states of acetonitrile are singlet, triplet and quintet spin state of acetonitrile have been considered for the study. The spectroscopic characterization viz. energy, geometrical parameters, infrared and electronic absorption spectra, molecular orbitals (MOs) their energies and natural transitions orbitals (NTOs) in gas phase and water solvent state reported at B3LYP/aug-cc-pVDZ level of theory. The second hyperpolarizability values are obtained using various methods and basis sets for comparison. It has been observed that the second hyperpolarizability values for the odd spin states of acetonitrile are more positive than the first hyperpolarizability. It is clearly seen that the effect of spin on spectroscopic parameters except on energy. The singlet gas phase acetonitrile calculations are well matching with the available experimental determinations. The TDDFT approach has been used to study electronic absorption spectra of all spin states of acetonitrile in gas phase and in water solvent. The IEFPCM model implemented in studying acetonitrile in water solvent at B3LYP/aug-cc-pVDZ level of theory. It is observed that HOMO to LUMO gap is larger for singlet than the triplet and quintet spin state and it decrease with an increase in strength of an applied field. All these calculations performed using Gaussian 16 program package.

Linear and nonlinear optical properties of some organoxenon derivatives

We employ a series of state-of-the-art computational techniques to study the effect of inserting one or more Xe atoms in HC2H and HC4H, on the linear and nonlinear optical (L&NLO) properties of the resulting compounds. It has been found that the inserted Xe has a great effect on the L&NLO properties of the organoxenon derivatives. We analyze the bonding in HXeC2H, and the change of the electronic structure, which is induced by inserting Xe, in order to rationalize the observed extraordinary L&NLO properties. The derivatives, which are of interest in this work, have been synthesized in a Xe matrix. Thus the effect of the local field (LF), due to the Xe environment, on the properties of HXeC2H, has also been computed. It has been found that the LF effect on some properties is significant. The calculations have been performed by employing a hierarchy of basis sets and the techniques MP2 and CCSD(T) for taking into account correlation. For the interpretation of the results we have employed the complete active space valence bond and CASSCF/CASPT2 methods.

Variational calculation of static and dynamic vibrational nonlinear optical properties

The vibrational configuration interaction method used to obtain static vibrational (hyper)polarizabilities is extended to dynamic nonlinear optical properties in the infinite optical frequency approximation. Illustrative calculations are carried out on H(2)O and NH(3). The former molecule is weakly anharmonic while the latter contains a strongly anharmonic umbrella mode. The effect on vibrational (hyper)polarizabilities due to various truncations of the potential energy and property surfaces involved in the calculation are examined.